The present invention relates to improvements made to hydraulic directional control valves having a regulating balance designed to sense the highest load pressure, assume an anti-saturation function and provide a function whereby the flow is split independently of the load, this balancing system comprising a plunger that can be displaced in a housing under the action of a differential pressure created by the intake pressure supplied by a hydraulic source applied to a first of its ends and by the highest load pressure applied to its other end, said plunger also being designed to open, in is proportion to the above-mentioned differential pressure, a lateral orifice of the housing connected to a working orifice of the directional control valve in order to apply hydraulic fluid thereto at the intake pressure less said differential pressure.
By way of example, FIG. 1 of the appended drawings illustrates in cross-section a known mode of operating such a directional control valve as disclosed in FIG. 1 of document FR-A 2 689 575.
The directional control valve has a body 1 provided with an orifice P for admitting pressurised fluid from a hydraulic source (not illustrated). In the example illustrated, said orifice P is provided in the form of a passage 2 crossing through the body 1, transversely to the plane of the drawing, and opening at the two main faces of said body, which acts as a support when several directional control valves are stacked side by side and one against the other. At least one orifice T (provided in the form of a passage crossing through the body 1 transversely to the plane of the drawing and opening at the two main faces of said body) is used to return the fluid to a tank (not illustrated). Two working orifices A, B can be connected to a hydraulic device or receiver (not illustrated). A slide valve 4 is designed to slide in a bore 5 which crosses longitudinally through the body 1 and opens at two opposing end faces 6, 7 thereof. In a conventional manner, the body 1 and the slide valve 4 have passages and/or ducts and/or grooves arranged so as to co-operate, with a view to establishing and/or cutting off the links between the various orifices P, A, B, T of the body of the directional control valve depending on the axial position occupied by the slide valve in the bore. The specific layout of these passages and/or ducts and/or grooves is determined by the person skilled in the art depending on the functions which the is directional control valve is required to perform.
In this specific example, the body 1 also has another transverse passage 8 extending between the main faces of the body and combined with at least one pressure selector, which enables the higher (load sensing pressure or LS pressure) of two pressures, these being the pressure in said passage upstream of the directional control valve and the working pressure of the directional control valve respectively, to be applied to a passage 18 located downstream of the slide valve 4.
In the bore 5 of the body, the passage 2 connected to the intake orifice P opens into an admission chamber 10 thereof, adjacent to which is another chamber 11 communicating via a passage 12 with a housing 13 in which a freely and tightly sliding plunger 14 is mounted. The passage 12 opens into the housing 13, at one end thereof, in this case the bottom end (corresponding to an end face of the plunger 14, in this case its bottom end) whilst at its opposite end (in this case its top end) the housing 13 opens into a cavity 15 in which the head 16 of the plunger 14 may be displaced. The head 16, which is wider than the body of the plunger, may bear on a shoulder provided at the point where the housing 13 opens into the cavity 15 in order to retain the plunger 14. A spring 17 is provided in the cavity 15 to push the plunger 14 back against said shoulder in order to fix its position in the absence of pressure. The above-mentioned passage 8 opens into the cavity 15 so that the pressure prevailing in the passage 8 is also present in the cavity 15 and hence applied to the corresponding end of the plunger 14 (in this case its top end).
In addition, the plunger 14 has passing through it an axial passage 18, opening at one end in its end face facing the passage 12 and at the other end in a diametral passage 19 crossing through the plunger 14 and arranged so that it is closed off by the wall of the housing 13 when the plunger 14 is in the rest position imposed by the spring 17 (illustrated in FIG. 1) or in a not fully raised position. A part 28 of the axial passage 18 is provided in the form of a restriction or a nozzle.
The portion of the slide valve 4 which, in the neutral position, extends between the chambers 10 and 11 isolating them from one another is provided with graded notches 20 designed to ensure that the hydraulic fluid flows in a controlled manner in the relevant direction when the slide is displaced in one direction or the other.
Extending from the housing 13 in two approximately diametrically opposed directions are two conduits 21, in one of which or in each of which a non-return valve 22 is arranged, the two conduits 21 opening, in the bore 5, into two respective chambers 23.
Close to the chambers 23, two respective distribution chambers 24 of the bore 5 are linked by conduits 25 to the respective working orifices or initial orifices A and B of the directional control valve.
Finally, beyond the distribution chambers 24, two return chambers 26 of the bore 5 are respectively linked by conduits 27 to the return passage 3 opening onto the return orifice T.
The way in which the directional control valve described above works is explained in detail in document FR 2 689 575, mentioned above, to which reference may be made.
Although a directional control valve of the design outlined above is satisfactory in terms its general operating principle, it nevertheless has a disadvantage under certain operating conditions. A directional control valve of this type is not designed to be used alone but to work in co-operation with several directional control valves of the same type to make up a multiple hydraulic directional control system. This being the case, the directional control valves are preferably stacked tightly one against the other by their main faces or large faces so that the respective conduits P, T and LS (passages 8) all communicate with one another and form continuous passages crossing through the stack from end to end, enabling the multiple directional control device to work.
In a multiple directional control device of this type, if operation of one particular distribution section (i.e. an individual directional control valve) is inhibited due to the action of a pressure LS imposed by another section of the multiple directional control device, it may nevertheless be desirable for that particular distribution section to be allowed to continue in operation so that the hydraulic receiver which it controls can be placed or maintained in operation, albeit at a reduced rate: this might be the case if a machine turret has to be rotated or a machine moved in translation, for example.
In other words, it would seem desirable to be able to impart an operating capability to a specific function, albeit at a lesser or downgraded rate, in spite of the controlled inhibiting action imposed by the general LS circuit of the multiple directional control device, and to do so without having to use a priority circuit for the specific section in question, examples of this being known, given that the use of such, which complicates the overall design and adds to the cost, does not seem to be called for in the context in question.
Accordingly, what is needed is to give the specific distribution section in question a pseudo-priority without substantially modifying the individual directional control valve or the multiple directional control device.